1. Field of the Invention
The present invention relates to a semiconductor fabricating method. More particularly, the present invention relates to a method of forming an alignment marker area.
2. Description of the Related Art
The purpose of a photolithographic process is to transfer a predetermined pattern onto a wafer. In order to transfer the predetermined pattern onto the wafer precisely, it is necessary to align the wafer before a photoresist exposure step takes place. In a wafer alignment procedure, trenches are first formed in specific areas of the wafer. The trenches are used to define an alignment marker area. The wafer alignment is obtained by detecting the reflection lights from the trenches in the alignment marker area.
FIGS. 1A through 1B are schematic, cross-sectional views of a conventional method of forming a dielectric layer in an alignment marker area.
In FIG. 1A, a wafer 100 having an alignment marker area 102 and a device area 104 is provided. The alignment marker area 102 includes trenches 102a and 102b formed in the wafer 100. The depth of the trenches 102a and 102b is about 1200 .ANG.. A device layer 106, which includes a variety devices (not shown), such as a silicon substrate, a source/drain region, a gate, etc., is formed on the wafer 100 in the device area 104.
In FIG. 1B, a metallic interconnection fabricating process is performed. A dielectric layer 108 is formed over the wafer 100. Commonly, the dielectric layer 108 is sufficiently transparent in a photolithographic process. The transparency of the dielectric layer 108 is advantageous to the alignment detection for the wafer 100. However, when the dielectric layer 108 is too thick, often thicker than 40000 .ANG., it is difficult to detect trenches 102a and 102b in the alignment marker area 102.